Evaluation of a new system for ventilatory administration of nitric oxide

Isocapnic hyperventilation provides early extubation after head and neck surgery: A prospective randomized trial

BACKGROUND

Isocapnic hyperventilation (IHV) shortens recovery time after inhalation anaesthesia by increasing ventilation while maintaining a normal airway carbon dioxide (CO2 )-level. One way of performing IHV is to infuse CO2 to the inspiratory limb of a breathing circuit during mechanical hyperventilation (HV). In a prospective randomized study, we compared this IHV technique to a standard emergence procedure (control).

METHODS

Thirty-one adult ASA I-III patients undergoing long-duration (>3 hours) sevoflurane anaesthesia for major head and neck surgery were included and randomized to IHV-treatment (n = 16) or control (n = 15). IHV was performed at minute ventilation 13.6 ± 4.3 L/min and CO2 delivery, dosed according to a nomogram tested in a pilot study. Time to extubation and eye-opening was recorded. Inspired (FICO2 ) and expired (FETCO2 ) CO2 and arterial CO2 levels (PaCO2 ) were monitored. Cognition was tested preoperatively and at 20, 40 and 60 minutes after surgery.

RESULTS

Time from turning off the vapourizer to extubation was 13.7 ± 2.5 minutes in the IHV group and 27.4 ± 6.5 minutes in controls (P < .001). Two minutes after extubation, PaCO2 was 6.2 ± 0.5 and 6.2 ± 0.6 kPa in the IHV and control group respectively. In 69% (IHV) vs 53% (controls), post-operative cognition returned to pre-operative values within 40 minutes after surgery (NS). Incidences of pain and nausea/vomiting did not differ between groups.

CONCLUSIONS

In this randomized trial comparing an IHV method with a standard weaning procedure, time to extubation was reduced with 50% in the IHV group. The described IHV method can be used to decrease emergence time from inhalation anaesthesia.

Evaluation of a method for isocapnic hyperventilation: a clinical pilot trial

BACKGROUND

Isocapnic hyperventilation (IHV) is a method that shortens time to extubation after inhalation anaesthesia using hyperventilation (HV) without lowering airway CO₂ . In a clinical trial on patients undergoing long-duration sevoflurane anaesthesia for major ear-nose-throat (ENT) surgery, we evaluated the utility of a technique for CO₂ delivery (DCO₂ ) to the inspiratory limb of a closed breathing circuit, during HV, to achieve isocapnia.

METHODS

Fifteen adult ASA 1-3 patients were included. After end of surgery, mechanical HV was started by doubling baseline minute ventilation. Simultaneously, CO₂ was delivered and dosed using a nomogram developed in a previous experimental study. Time to extubation and eye opening was recorded. Inspired (FICO₂ ) and expired (FETCO₂ ) CO₂ and arterial CO₂ levels were monitored during IHV. Cognition was tested pre-operatively and at 20, 40 and 60 min after surgery.

RESULTS

A DCO₂ of 285 ± 45 ml/min provided stable isocapnia during HV (13.5 ± 4.1 l/min). The corresponding FICO₂ level was 3.0 ± 0.3%. Time from turning off the vaporizer (1.3 ± 0.1 MACage) to extubation (0.2 ± 0.1 MACage) was 11.3 ± 1.8 min after 342 ± 131 min of anaesthesia. PaCO₂ and FETCO₂ remained at normal levels during and after IHV. In 85% of the patients, post-operative cognition returned to pre-operative values within 60 min.

CONCLUSIONS

In this cohort of patients, a DCO₂ nomogram for IHV was validated. The patients were safely extubated shortly after discontinuing long-term sevoflurane anaesthesia. Perioperatively, there were no adverse effects on arterial blood gases or post-operative cognition. This technique for IHV can potentially be used to decrease emergence time from inhalation anaesthesia.

Inhaled nitric oxide therapy in neonates and children: reaching a European consensus

Inhaled nitric oxide (iNO) was first used in neonatal practice in 1992 and has subsequently been used extensively in the management of neonates and children with cardiorespiratory failure. This paper assesses evidence for the use of iNO in this population as presented to a consensus meeting jointly organised by the European Society of Paediatric and Neonatal Intensive Care, the European Society of Paediatric Research and the European Society of Neonatology. Consensus Guidelines on the Use of iNO in Neonates and Children were produced following discussion of the evidence at the consensus meeting.

The use of inhaled prostacyclin in nitroprusside-resistant pulmonary artery hypertension

Because nitroprusside NTP infusion used to differentiate between fixed and reversible pulmonary artery hypertension in heart transplant candidates can result in systemic hypotension before reducing pulmonary artery pressures, we observed the effect or inhaled prostacyclin (PGI(2)) on pulmonary artery pressures and transpulmonic gradient (TPG) in patients with NTP-resistant pulmonary artery hypertension. Six patients undergoing evaluation for orthotropic heart transplant (OHTX) with NTP-resistant pulmonary artery hypertension received inhaled PGI(2), with hemodynamic measurements made at baseline, on NTP- and PGI(2) inhaled after returning to baseline. Compared with hemodynamic results with NTP, inhaled PGI(2) caused significant decrease in pulmonary artery systotic pressure, 43.8 +/- 4.8 mm Hg vs 63.2 +/- 2.04 mm Hg (p < 0.001); Mean pulmonary artery pressure, 22.7 +/- 4.18 vs 32.3 +/- 3.39 mm Hg (p < 0.05); and TPG, 11.5 +/- 3.73 vs 17.0 +/- 4.69 mm Hg (p < 0.05), with a 40% decrease in pulmonary vascular resistance/systemic vascular resistance ratio. We conclude that inhaled PGI(2) has benefit in reversing pulmonary artery hypertension resistant to NTP, in patients undergoing OHTX evaluation which is due to its more selective pulmonary vasodilation.

An evaluation of nitric oxide and nitrogen dioxide absorbers and filters

The absorbance of NO (5-90 ppm) and NO2 (0.5-4 ppm) by a number of absorbers and filters was assessed via bench testing. All absorbers (Sodasorb, Purafil CP, Purafil Select, Sofnolime, Sofnofil and 50/50 mix of Sofnolime/Sofnofil) except Sodasorb absorbed NO almost completely. Only Sofnolime absorbed NO2 completely while Sodasorb and the Sofnolime/Sofnofil 50/50 mix had absorbances between 47% and 90%. The absorbance of four filters (ILF100, ILF150, ILF200 and HgCONO) as well as Sofnolime and the Sofnolime/Sofnofil 50/50 mix was tested in the expiratory port of a Servo 900C ventilator All absorbers and filters produced a change in ventilator pressures. The HgCONO filter Sofnolime and the Sofnolime/Sofnofil 50/50 mix all absorbed NO. At 80 ppm NO, the HgCONO filter had 100% absorbance for four hours while Sofnolime's absorbance was significantly reduced after one hour. All filters and absorbers tested on the ventilator except the Sofnolime/Sofnofil 50/50 mix and the ILF150 filter absorbed NO2 completely for a period ranging from 90 minutes to four hours. We recommend the HgCONO filter and Sofnolime to absorb both NO and NO2. If absorption of NO2 only is required we recommend the HgCONO, ILF100 or ILF200 filters or the Sofnolime absorber.

During neonatal mechanical ventilatory support, the delivered nitric oxide concentration is affected by the ventilatory setting

OBJECTIVE

To assess whether the delivered nitric oxide (NO) concentration is affected by a change in the ventilatory setting during neonatal mechanical ventilatory support.

DESIGN

Prospective, experimental study.

SETTING

Laboratory at Nagoya City University Medical School.

INTERVENTIONS

This study was performed by using a pressure-limited, time-cycled, ventilatory support with a neonatal circuit and a 50-mL silicone test lung. NO in N2 gas was administrated into the inspiratory limb at a distance of 4 cm, 80 cm, or 160 cm from the Y piece connected to the adapter of an endotracheal tube. The NO concentration was measured every 0.5 sec by a chemiluminescence analyzer at the Y piece.

MEASUREMENT AND MAIN RESULTS

NO concentrations were compared with each of the ventilatory settings of peak inspiratory pressure (PIP) (10-30 cm H2O), positive end-expiratory pressure (0-10 cm H2O), ventilatory flow (10, 20, 30 L/min), and ventilatory rate (30, 40, 50, 60, 70 breaths/min), respectively. The NO concentration was significantly lower when NO was added at 4 cm than at 80 cm or 160 cm from Y piece at the same ventilatory setting of PIP, positive end-expiratory pressure and ventilatory flow, respectively, (p < .01). Although the NO concentration was increased as the settled PIP level was increased (p < .01 or p < .05), it was not changed when the settled positive end-expiratory pressure level was increased. A decrease was seen in the NO concentration as the settled ventilatory flow was increased (p < .01). Lastly, the NO concentration fluctuated greatly in association with the settled ventilatory rate.

CONCLUSION

The NO concentration delivered to patients is influenced by the ventilatory setting during neonatal mechanical ventilatory support.

Inhaled nitric oxide fraction is influenced by both the site and the mode of administration

OBJECTIVE

Inhaled nitric oxide (NO) can be delivered continuously or sequentially (= during inspiration) at different locations of the ventilation circuit. We have tested the influence of locations, modes of NO administration and the ratio of the inspiratory time over the respiratory cycle time (I/I + E ratio) on the accuracy of NO fractions, delivered by 2 devices: Opti-NO and Flowmeter.

METHODS

We used a simplified lung model consisting of a ventilation circuit with a Y piece, a tracheal tube, a 150 ml dead-space volume and a 5 liter balloon. Three fractions (3, 6, 9 ppm) were administered continuously or sequentially, in controlled volume, in 4 different sites on the inspiratory branch above the Y piece: i) just after the water trap, ii) just before the Y piece; below the Y piece: iii) just after the Y piece, iv) into the endotracheal tube. In addition, different I/I + E ratios (25, 33, 50, 80%) were studied. The delivered NO fractions were measured in the balloon by chemiluminescence (CLD 700, Ecophysics). A linear regression analysis was used to test the relationship between administered and measured NO fractions for the 3 fractions (3, 6 and 9 ppm) in sequential and continuous modes. Intercept values were compared to zero and slopes to the identity line.

RESULTS

When NO was administered in the continuous mode upstream the Y piece, NO fractions measured in the balloon corresponded to the administered fractions. In contrast, below the Y piece, the measured NO fractions were significantly lower than the administered NO fractions. In the sequential mode, above and below the Y piece, the delivered NO fractions were within the manufacturer's range.

CONCLUSIONS

For the continuous NO delivery, locations above the Y piece are mandatory. However, locations below the Y piece imposes a sequential system, which can also be used for the sites located above the Y piece.

Effect of nitric oxide predilution on inhaled nitrogen dioxide concentrations

We examined the possibility that predilution of a concentrated nitric oxide (NO) source with nitrogen, before contact with oxygen, can reduce the inspired nitrogen dioxide (NO2) concentration during administration of nitric oxide. A Manley Blease and a Siemens Servo 900 C ventilator delivered 10, 20, 40, 60 and 80 parts per million (ppm) NO using an NO source of 1000, 400 and 200 ppm. With the Manley Blease system, predilution from 1000 to 200 ppm NO reduced the inhaled NO2 concentration from 0.14 to 0.05 ppm (p < 0.01) at 10 ppm inhaled NO, and from 1.20 to 1.00 ppm (p < 0.01) at 40 ppm inhaled NO. With the Siemens Servo 900 C ventilator, inspiratory NO2 concentrations decreased from 0.21 to 0.11 ppm (p < 0.01) at 10 ppm inhaled NO, and from 1.49 to 1.16 ppm (p < 0.01) at 40 ppm NO. Predilution from 1000 to 400 ppm NO reduced the inspired NO2 concentrations by < 3% using either ventilator when the inspirated NO concentration was 80 ppm. Predilution of NO with nitrogen significantly reduced the inspired NO2 concentrations for nitric oxide concentrations between 10 and 40 ppm, but offered no clinically relevant advantage at higher NO concentrations.

Minimizing the inhaled dose of NO with breath-by-breath delivery of spikes of concentrated gas

BACKGROUND

Pulmonary vasodilatation with a 100 ppm concentration of NO given as a short burst of a few milliliters at the beginning of each breath (NOmin) was compared with conventionally inhaled NO, in which a full breath of 40 ppm of NO was inhaled (NOCD).

METHODS AND RESULTS

NOmin was studied in 16 patients with severe pulmonary hypertension and in 16 isolated porcine lungs with experimentally induced pulmonary hypertension. We compared volumes of 8 to 38 mL of 100 ppm NO in N2 injected at the beginning of each breath with conventional inhalation of 40 ppm NO in air. NOCD and NOmin were studied in 4 pigs after inhibition of NO synthase with NG-nitro-L-arginine methyl ester (1 to 2 mg/kg IV) had raised the pulmonary vascular resistance index (PVRI) from 4.4+/-0.8 to 10. 0+/-1.6 mm Hg. L-1. min-1. kg-1. A similar comparison was made in 7 isolated porcine lungs after the thromboxane analogue U46619 (10 pmol. L-1. min-1) increased the mean PVRI from 4.6+/-0.8 to 12.2+/-1. 3 mm Hg. L-1. min-1. kg-1. Patients' mean PVRI was reduced from 29. 2+/-3.7 to 24.0+/-3.1 with NOmin and 24.5+/-3.3 mm Hg. L-1. min-1. m-2 (mean+/-SEM) with NOCD. In isolated porcine lungs, there was the same reduction of PVRI for NOmin and NOCD between 12.7% and 34.8%.

CONCLUSIONS

A small volume of NO inhaled at the beginning of the breath was equally effective as NOCD but reduced the dose of NO per breath by 40-fold, which ranged from 1.2x10(-8) (0.4 microg) to 1. 6x10(-7) mol/L (4.8 microg) compared with 5.3x10(-7) (16 microg) to 1.2x10(-6) mol/L (36 microg) per breath with NOCD.

Comparison of inhaled nitric oxide and inhaled aerosolized prostacyclin in the evaluation of heart transplant candidates with elevated pulmonary vascular resistance

STUDY OBJECTIVE

Elevated pulmonary vascular resistance is a risk factor in heart transplantation and reversibility of high pulmonary vascular resistance is evaluated preoperatively in potential recipients using i.v. vasodilators or inhaled nitric oxide. Prostacyclin is a potent vasodilator, which when inhaled, has selective pulmonary vasodilatory properties. The aim of this study was to compare the central hemodynamic effects of inhaled prostacyclin with those of inhaled nitric oxide in heart transplant candidates.

DESIGN

A pharmacodynamic comparative study.

SETTING

Cardiothoracic ICU or laboratory for diagnostic heart catheterization at a university hospital.

PATIENTS

Ten heart transplant candidates with elevated pulmonary vascular resistance (>200 dynes x s x cm(-5) and/or a transpulmonary pressure gradient > 10 mm Hg) were included in the study.

INTERVENTIONS

Nitric oxide (40 ppm) and aerosolized prostacyclin (10 microg/mL) were administered by inhalation in two subsequent 10-min periods. Hemodynamic measurements preceded and followed inhalation of each agent.

MEASUREMENTS AND RESULTS

Both inhaled nitric oxide and inhaled prostacyclin reduced mean pulmonary artery pressure (-7% vs -7%), pulmonary vascular resistance (-43% vs -49%), and the transpulmonary gradient (-44% vs -38%). With inhaled prostacyclin, an 11% increase in cardiac output was observed. Other hemodynamic variables, including the systemic BP, remained unaffected by each of the agents.

CONCLUSIONS

Inhaled prostacyclin induces a selective pulmonary vasodilation that is comparable to the effect of inhaled nitric oxide. Major advantages with inhaled prostacyclin are its lack of toxic reactions and easy administration as compared with the potentially toxic nitric oxide requiring more complicated delivery systems.

Nitric oxide inhalation therapy for newborn infants

Binding of NO to heavy metal-containing proteins probably accounts for many of its physiologic actions. NO inhalation is a promising new treatment for various disorders of neonates. The therapy is most likely to benefit premature neonates who are hypoxemic despite breathing pure oxygen and those who suffer from impaired carbon dioxide elimination. Newborn infants who have congenital heart disease may benefit from inhaled NO therapy if their disease involves some form of pulmonary venous hypertension or if they have recently undergone surgery involving cardiopulmonary bypass grafting. The use of NO in infants with PPHN might obviate the need for ECMO or other invasive treatment methods. Neonates with CDH seem likely to benefit marginally from NO therapy. Minimizing the toxicities of NO inhalation therapy requires that the physicians understand the nuances of infant care. The therapeutic value of increasing carbon dioxide elimination with NO inhalation warrants further investigation.

[Inhaled nitric oxide in anesthesia and intensive care]

The role of endothelium in vascular relaxation is linked to the existence of endothelium derived relaxing factors (EDRF) known since 1980. In 1987, nitric oxide (NO) was identified as one of these factors. NO acts in many physiologic and pathophysiologic events. Atmospheric NO is a pollutant. Inhaled NO allows selective pulmonary vasodilation and is used to treat pulmonary artery hypertension (PAH). As inhaled NO is inactivated immediately in the blood by linking to haemoglobin, systemic vasodilation does not occur and right ventricular coronary perfusion pressure does not decrease. This is particularly important in the treatment of right ventricular failure due to PAH following cardiothoracic surgery. In patients with an acute respiratory distress syndrome (ARDS), inhaled NO improves the perfusion of adequately ventilated pulmonary territories. Very low concentrations of NO, such as two parts per million, decrease intrapulmonary venous admixture and may reverse hypoxaemia. However its long term benefits in ARDS must be assessed more accurately with multicentre controlled studies. Inhaled NO also improves refractory hypoxaemia in neonates. Its bronchodilatory effect, demonstrated experimentally, does not occur in acute obstructive bronchopulmonatory disease. The toxicity of NO, and overall of its oxidated derivative NO2 requires precise conditions of administration and close monitoring of inhaled fractions. In that case, the risk of NO toxicity seems very low when compared to its therapeutic benefits in selected patients.

Induction of chromosome aberrations in peripheral blood lymphocytes after short time inhalation of nitric oxide

INTRODUCTION

inhalation of nitric oxide (INO) leads to vasodilation of pulmonary vasculature in ventilated regions of the lung. The clinical use of INO, although not formally approved as a drug, is widespread. NO may rapidly form nitrogen dioxide (NO2) in an oxygen containing gas mixture. NO2 has been shown to induce chromosome aberrations and mutations in both animal and bacterial test systems. We investigated whether a 2-h exposure to NO would increase frequencies of cells with chromosome aberrations in peripheral blood lymphocytes of human volunteers.

METHODS

10 volunteers were exposed to inhaled NO 40 parts per million (ppm) for 2 h. Pre- and post-exposure blood samples were analysed.

RESULTS

no statistically significant differences (p</=0.05) in chromosome aberrations were observed between pre- and post-exposure samples.

CONCLUSION

no detectable increase of chromosome aberrations in human peripheral blood lymphocytes after 2 h of NO-inhalation 40 ppm was found.

Inhaled nitric oxide: technical aspects of administration and monitoring

OBJECTIVES

Clinical applications of inhaled nitric oxide (NO) therapy resulted in the development of delivery systems and monitoring devices applicable to routine clinical care. This article presents the various components necessary for an adequate clinical use of inhaled NO, and discusses the NO gas mixture cylinders, inhaled NO delivery techniques and specifications, monitoring devices, and ending with an exhaustive description of the scavengers of nitrogen oxides (NOx).

DATA SOURCES

Computerized search (CURRENT CONTENTS, MEDLINE) of published original research and review articles (approximately 200), conference abstracts and compendiums up to May 1997 (approximately 50), personal files, and contact with expert informants.

STUDY SELECTION

Technical, experimental, and clinical reports were selected from the recent English, French, German, and Spanish literature, if pertinent to the administration or monitoring of inhaled NO.

DATA EXTRACTION

The authors extracted all applicable data.

DATA SYNTHESIS

The production of NO gas mixture cylinders must be certified with respect to gas purity, stability, and concentration (limits between 100 and 1000 ppm), guaranteed calibration, and specific color. An ideal inhaled NO delivery device requires a synchronized delivery, a minimal production of nitrogen dioxide (NO2), and should be simple to use (verification, calibration, convenient flushing, cylinder change possible while in use and a simple alarm setting) with full information (high and low alarms and available precision monitoring of NO, NO2, and O2). Emergency and transport systems must be readily available. The choice of the monitoring device (chemiluminescence or electrochemistry) should be made based on the knowledge of their strength and weakness for a particular clinical application. Finally, scavengers of NOx should be used with caution until specific filters are proven safe and effective.

CONCLUSIONS

The great expectancies generated by inhaled NO action have led researchers to design personal inhaled NO delivery systems, but only with mitigated results. At present, medical companies are finding a financial interest in designing a delivery system which will suit the needs of clinicians and this, along with official governmental approval, will only then permit the use of inhaled NO safely and on a larger scale.

Propagation of nitric oxide pools during controlled mechanical ventilation

OBJECTIVE

Infusing nitric oxide at a constant rate into a breathing circuit with intermittent mainstream flow causes formation of nitric oxide pools between successive breaths. We hypothesized that incomplete mixing of these pools can confound estimates of delivered nitric oxide concentrations.

METHODS

Nitric oxide flowed at a constant rate into the upstream end of a standard adult breathing circuit connected to a lung model. One-milliliter gas samples were obtained from various sites within the breathing system and during various phases of the breathing cycle. These samples were aspirated periodically by a microprocessor controlled apparatus and analyzed using an electrochemical sensor.

RESULTS

The pools of nitric oxide distorted into hollow parabolic cone shapes and remained unmixed during their propagation into the lungs. In our preparation, time-averaged nitric oxide concentrations were minimal 60 cm downstream of the infusion site (18 ppm) and maximal 15 cm upstream of the Y-piece (36 ppm). The concentrations were mid-range within the lung (23 ppm), yet were substantially less than predicted by assuming homogeneity of the gases (31 ppm). Generally, nitric oxide concentrations within the lung were different from all other sites tested.

CONCLUSION

Incomplete mixing of nitric oxide confounds estimates of delivered nitric oxide concentrations. When nitric oxide is infused at a constant rate into a breathing circuit, we doubt that any sampling site outside the patient's lungs can reliably predict delivered nitric oxide concentrations. Strategies to ensure complete mixing and representative sampling of nitric oxide should be considered carefully when designing nitric oxide delivery systems.

Intratracheal instillation of a novel NO/nucleophile adduct selectively reduces pulmonary hypertension

We examined the pulmonary and systemic hemodynamic effects of administering soluble nitric oxide (NO) donor compounds (NO/nucleophile adducts, i.e., NONOates) directly into the trachea of animals with experimentally induced pulmonary hypertension. Steady-state pulmonary hypertension was created by using the thromboxane agonist U-46619. Yorkshire pigs were randomly assigned to one of four groups: group 1, intratracheal saline (control; n = 8); group 2, intratracheal sodium nitroprusside (n = 6); group 3, intratracheal ethylputreanine NONOate (n = 6); and group 4, intratracheal 2-(dimethylamino)-ethylputreanine NONOate (DMAEP/NO; n = 6). Pulmonary and systemic hemodynamics were monitored after drug instillation. Group 4 had significant reductions in pulmonary vascular resistance index (PVRI) at all time points compared with steady state and compared with group 1 (P < 0.05), whereas systemic vascular resistance index did not change. The mean change in mean pulmonary arterial pressure in group 4 was -33.1 +/- 1.2% compared with +6.4 +/- 1.3% in group 1 (P < 0.001), and the mean change in mean arterial pressure was -9.3 +/- 0.7% compared with a control value of -0.9 +/- 0.5% (P < 0.05). Groups 2 and 3 had significant decreases in both PVRI and systemic vascular resistance index compared with steady state and with group 1. In conclusion, intratracheal instillation of a polar-charged tertiary amine NONOate DMAEP/NO results in the selective reduction of PVRI. Intermittent intratracheal instillation of selective NONOates may be an alternative to continuously inhaled NO in the treatment of pulmonary hypertension.

A retrospective analysis of nitric oxide inhalation in patients with severe acute lung injury in Sweden and Norway 1991-1994

BACKGROUND

Patients with severe acute lung injury (ALI) have been treated compassionately on doctors' initiative with inhaled nitric oxide (INO) in Sweden and Norway since 1991. In 1994 the previously used technical grade nitric oxide was replaced by medical grade nitric oxide.

METHODS

We have carried out a retrospective data collection on all identified adult patients treated with INO for >4 h during the period 1991-1994 focusing on safety aspects and patient outcome. We used the following exclusion criteria (1) Age <18 years, (2) Simultaneous treatment with extracorporeal removal of CO2 (3) NO inhalation period <4 h, (4) Incomplete or missing patient charts, (5) Use of INO in order to treat pulmonary hypertension following cardiac surgery, with little or no acute lung injury.

RESULTS

Inclusion criteria were met by 56 out of 73 identified patients. Mean age was 48+/-19 years and the median duration of INO treatment was 102 h. PaO2/FIO2 ratio at start of treatment was 85 +/- 33 mm Hg with a lung injury score (LIS) of 3.2+/-0.8. The aetiology of the lung injury was pneumonia (n= 27), sepsis (n=12) and trauma (n=8). Survival to hospital discharge was 41% and survival after 180 d was 38%. Three serious adverse events were identified, two from technical failures of the INO delivery device and one withdrawal reaction necessitating slow weaning from INO. No methaemoglobin values >5% were reported during treatment.

CONCLUSION

The overall mortality did not differ dramatically from historical controls with high mortality. Only a randomised study may determine whether INO as an adjunct to treatment alters the outcome in severe ALI. One cannot at present advocate the routine use of INO in patients with ALI outside such studies.

Uptake of inhaled nitric oxide in acute lung injury

BACKGROUND

Despite the widespread use of inhaled nitric oxide (NO), little is known of its pulmonary uptake in patients with acute respiratory failure.

METHODS

Fourteen patients with acute lung injury (ALI) and ongoing NO therapy were studied. Three doses of NO (5, 10 and 40 ppm) were given for 20 min and at each dose level the following parameters were recorded: minute ventilation, inspiratory NO conc., mixed expired NO conc., end-tidal NO conc., mixed expired CO2 conc., end-tidal CO2 conc, and arterial CO2 tension. Total uptake was calculated and correlated to the total amount of NO inhaled, the amount of NO administered to the alveolar space, and the amount of NO administered to the perfused alveolar space.

RESULTS

About 35% of the total amount of NO delivered is taken up by the lungs, 70% of NO administered to the alveolar space is taken up, and 95-100% of the NO administered to perfused alveolar space is taken up. The size of the alveolar dead space varied between 10 and 60% of the alveolar space. At 40 ppm of inhaled NO there was no difference between inspired and mixed expired NO2 concentration, indicating that there is no significant NO2 formation taking place in the lungs during NO inhalation at the concentrations studied.

CONCLUSIONS

Practically all NO administered to the perfused alveolar space is taken up. The total uptake differs from that of healthy persons probably because of differences in the alveolar dead space.

Behavior of nitric oxide infused at constant flow rates directly into a breathing circuit during controlled mechanical ventilation

OBJECTIVES

This study was designed to test the hypothesis that the practice of infusing nitric oxide at constant flow rates directly into breathing circuits with intermittent (pulsatile) flow can lead to streaming and tidal pooling of the nitric oxide. This study was also designed to show the extent to which streaming and tidal pooling of nitric oxide affect nitric oxide delivery.

DESIGN

A series of five in vitro experiments was performed. For each experiment, either one or two features of the nitric oxide delivery/sampling system were varied, and the effects of these variations were evaluated with regard to measured nitric oxide concentration changes. The results from each experiment were analyzed using either one- or two-factor analysis of variance.

SETTING

University research laboratory.

SUBJECTS

Breaths were provided by a mechanical ventilator that was connected to a lung model. A standard, corrugated, adult breathing circuit was used. Gas samples were obtained from either the lung model's bellows or selected sites within the breathing circuit. Nitric oxide concentrations were measured, using an electrochemical gas analyzer.

INTERVENTIONS

The system features that were varied included the cross-sectional position of the sampling site within the breathing circuit, the distance between the infusion port and the sampling site, the breathing frequency, the distance between the Y-piece and the infusion port, and the airway (deadspace) volume.

MEASUREMENTS AND MAIN RESULTS

Streaming of nitric oxide within the breathing circuit was detected as far as 25 cm downstream of the infusion site (p < .0001). Pooling of nitric oxide was detected both near and downstream of the infusion site (p < .0001). Increasing the breathing frequency from 5 to 30 breaths/min increased mixing thoroughness (p < .005). Increasing the distance between the Y-piece and the infusion port from 15 to 180 cm decreased nitric oxide delivery to our lung model (p < .0001). Interestingly, increasing airway (deadspace) volume from 150 to 450 mL decreased nitric oxide delivery to our lung model (p < .0001).

CONCLUSIONS

Estimates of nitric oxide delivery using a constant flow rate of nitric oxide infused directly into a breathing circuit during controlled mechanical ventilation can be confounded by streaming and tidal propagation of nitric oxide pools. Improved reproducibility of reported dose-response relationships is likely to be achieved through further study of nitric oxide behavior within the breathing circuits. Reduced toxicity associated with nitric oxide inhalation may also be achieved through a better understanding of this nitric oxide behavior.

Nitric oxide administration after the ventilator: evaluation of mixing conditions

BACKGROUND

Because of the potential toxicity of nitric oxide (NO) and its oxidising product nitrogen dioxide (NO2), any system for the delivery of inhaled NO must aim at stable and predictable levels of NO and as low concentrations as possible of NO2.

METHODS

In a laboratory set-up, we have evaluated mixing conditions in a system where NO is added after the ventilator with continuous flow. Mixing was studied by using carbon dioxide (CO2) as a tracer gas since capnography has a short response time (360 ms) in comparison with measurements of NO with electrochemical fuel cells (response time of 18 s). CO2 (in volumes corresponding to an ideal mixture of 1, 3 and 6%) was fed, after the ventilator, either into plain breathing tubing, into one or two soda lime absorbers, or into an empty and a soda lime-filled canister, at different ventilatory rates and different I:E ratios. Samples were drawn from the inspiratory limb close to the Y-piece. NO was added in the same way and in the same volume as the highest concentration of CO2.

RESULTS

CO2 added to plain tubing resulted in peak levels up to five times the set levels, while addition to a mixing box with an empty and a soda lime-filled canister resulted in even mixing with gas concentrations close to the ideal. When NO was fed into plain tubing, low levels were measured at the Y-piece, indicating poor mixing. Gas supply to a mixing chamber resulted in even concentrations.

CONCLUSION

Even and predictable levels of NO can be obtained with continuous flow of NO to the inspiratory limb, after the ventilator, if a mixing chamber is used. To obtain adequate mixing, the volume of the mixing box should be greater than the tidal volume.

A delivery system for inhalation of nitric oxide evaluated with chemiluminescence, electrochemical fuel cells, and capnography

OBJECTIVE

To evaluate a system for delivery of inhaled nitric oxide.

DESIGN

Prospective, laboratory study.

SETTING

Engineering laboratory.

SUBJECTS

A standard ventilator (Servo Ventilator 300), supplemented with extra gas modules for nitric oxide delivery.

INTERVENTIONS

Two ventilator-integrated gas modules, delivering < or = 10 parts per million (ppm) or < or = 100 ppm of nitric oxide, were used in adult and neonatal modes during volume-controlled ventilation. Set nitric oxide concentration and FIO2 were systematically changed and compared with the measured concentration. Short-term mixing was tested in adult, pediatric, and neonatal modes by substituting nitric oxide with CO2, and measuring the delivered concentration by a fast-response CO2 analyzer during five successive respiratory cycles. Long-term mixing was tested with the administration of 25 ppm of nitric oxide for 7 days.

MEASUREMENTS AND MAIN RESULTS

Delivered concentration of nitric oxide and nitrogen dioxide were simultaneously measured at the Y-place by two methods-chemiluminescence and electro-chemical fuel cells. The maximum absolute difference between set and measured concentrations of nitric oxide in the adult mode was 0.6 ppm at a set concentration of 10 ppm and 2.7 ppm at a set concentration of 100 ppm. In the neonatal mode, the maximal difference was 3.1 ppm at a set concentration of 100 ppm. Nitrogen dioxide concentration increased with increasing concentration of nitric oxide and oxygen to 2.6 ppm (as measured by the chemiluminescence analyzer) and 3.6 ppm (as measured by the electro-chemical fuel cell), at a setting of 100 ppm of nitric oxide with an FIO2 of 0.90 in the neonatal mode (2 L/min). During the short-term test of mixing stability throughout the respiratory cycles, a constant set CO2 concentration varied maximally by +/-6.2% from the set value in the neonatal mode, whereas the variance was by +/-6.5% in pediatric mode, and by +/-8.0% in the adult mode. During the long-term test, nitric oxide concentration varied maximally by +/-2.6% (as measured by the chemiluminescence analyzer) and by +/-2.3% (as measured by the electrochemical fuel cell).

CONCLUSIONS

An accurate precision in delivered nitric oxide concentration was achieved during intermittent flow ventilation, and this accuracy was independent of tested ventilator settings. The delivery system administered an almost stable concentration throughout a respiratory cycle and during long-term delivery. If the mixing point is in the inspiratory part of the ventilator, valid measurement of nitric oxide and nitrogen dioxide delivery concentrations are possible. Both techniques for measuring nitric oxide and nitrogen dioxide have drawbacks.

A safe clinical system for nitric oxide inhalation therapy for pediatric patients

A safe clinical system for nitric oxide (NO) inhalation therapy was developed. The system consists of three parts: a NO controller, a NO monitor, and a patient circuit. NO gas flow and carrier gas flow are controlled by a special rust-proof thermal mass flowmeter. Standard gas quality NO gas (10,000 ppm, balance nitrogen) is used. The outlet of the NO gas tank is connected to the distal end of a heated humidifer that is very close (12 mL) to the patient, to decrease acidic water precipitation and decrease contact time between NO and oxygen (O2). Fail-safe mechanisms to prevent the delivery of a hypoxic mixture or excessive NO concentration are incorporated. Inspiratory NO concentration is continuously monitored by a modified electrochemical NO meter. The patient circuit consists of a breathing circuit and a ventilator with a scavenging unit. A modified Mapleson D type circuit is used. Fresh gas, humidified and mixed with NO, is introduced to the patient connection port. A mechanical ventilator, either of conventional or of high-frequency oscillation type, is connected to the expiratory limb of the Mapleson D circuit. A coaxial scavenging unit including activated charcoal is placed in between the expiratory limb and the ventilator. The adjustment of inspiratory NO concentration (y) was accurate over a wide range (1-80 ppm) of concentrations (x) (y = 0.36 + 0.96x, R2 = 0.999, n = 45) and showed good agreement with the chemiluminescence method. Inspiratory nitrous oxide (NO2) concentration was less than 0.3 ppm, and acidic water accumulation as measured by NO2- and NO3- was less than 5 ppm, even at an extremely high NO concentration of 80 ppm with an FiO2 of 1.0 and 10 L/min of fresh gas flow. Environmental NO and NO2 concentrations in the ICU remained below 0.005 and 0.05 ppm, respectively. This system was used clinically on 214 pediatric patients and proved to be accurate, safe, and useful.

Response to nitric oxide inhalation in early acute lung injury

OBJECTIVE

To evaluate the dose response of inhaled nitric oxide (NO) on gas exchange and central haemodynamics in patients with early acute lung injury (ALI).

DESIGN

Prospective, multicentre clinical study.

SETTING

General ICUs in university and regional hospitals.

PATIENTS

18 Patients with early ALI according to specified criteria.

INTERVENTIONS

During controlled ventilation an inhalation system was used to deliver NO (1000 ppm in N2) and O2/air to the low pressure fresh gas inlet of a Siemens 900C ventilator. Haemodynamics and pulmonary gas exchange variables were measured at baseline and at stepwise increased inspiratory NO concentrations of 0.1, 0.3, 1, 3, 10, 30 and 100 ppm, each dose being maintained for 15 min. Dose testing was repeated the next day, and the response to prolonged (2 h) NO inhalation at 1 and 10 ppm was also tested.

MEASUREMENTS AND RESULTS

Inhalation of NO produced a significant increase in PaO2 (P < 0.0025). The degree of response, as well as the optimal NO dose varied in individual patients and between different days. Venous admixture (QVA/QT) was reduced (P < 0.02) from 38% (31-46%) to 33% (26-41%). In our patients with early acute lung injury and only a moderate elevation in pulmonary arterial pressure NO inhalation did not reduce mean pulmonary artery pressure significantly, being 27.0 (21-30) mmHg at baseline and 26.0 (21-30) mm Hg at 100 ppm.

CONCLUSIONS

This study shows that improvements in arterial oxygenation in response to inhaled NO may show great inter- as well as intraindividual variability, and that improvements in arterial oxygenation occur without any measurable lowering of the pulmonary artery pressure.

Safety aspects of delivery and monitoring of nitric oxide during mechanical ventilation

In the presence of oxygen NO is oxidised to NO2, which is toxic in higher concentrations. In this technical investigation, we evaluated a dosage system, modified from Stenqvist et al. 1993 (1), regarding NO and NO2 levels. NO was administered before the ventilator and NO2 scavenged using a soda little absorber in the inspiratory limb close to the ventilator. NO/NO2 levels were measured using fuel cell technique. We tested the duration of soda lime scavenging, put in additional soda lime absorbers, used charcoal as absorber and exchanged tubing material. NO was delivered after the ventilator and we studied effect of interruption of ventilation. With concentrations of NO at or below 40 parts per million (ppm) at F1O2 0.9, NO2 levels were 1.2 ppm or lower. Corresponding values for 20 and 10 ppm were 0.4 and 0.2 ppm, respectively. Duration of the soda lime absorber was at least 72 hours. Additional soda lime absorbers did not further reduce NO2 levels. Charcoal absorbers reduced NO2, but also NO by 45% from set value. Tubing materials had no influence on NO and NO2 levels. When administering NO at the Y-piece, levels of NO were increased by 35-60% and NO2 levels by 110-230% compared to set values. Oxidation of NO to NO2 is continuously taking place in the breathing system. Doses of up to 40 ppm NO should be considered safe regarding NO2 levels. Administration of NO at the Y-piece gives high and unpredictable levels of NO2.

Inhaled nitric oxide in children with severe lung disease: results of acute and prolonged therapy with two concentrations

OBJECTIVES

To evaluate the acute effects of 11 and 60 parts per million (ppm) inhaled nitric oxide on the pulmonary vascular resistance and systemic oxygenation of children with severe lung disease, and to compare the outcome of prolonged therapy with approximately 10 and 40 ppm inhaled nitric oxide.

DESIGN

Prospective, randomized study.

SETTING

A 26-bed pediatric intensive care unit in a tertiary children's hospital.

PATIENTS

Nineteen patients (median age 11 yrs, range 7 months to 16 yrs) with acute bilateral lung disease requiring a positive end-expiratory pressure (PEEP) of > 6 cm H2O and an FIO2 of > 0.5 for > 12 hrs were treated with inhaled nitric oxide. One patient was treated twice during the same hospitalization.

INTERVENTIONS

Acute hemodynamic and blood gas effects of 11 and 60 ppm inhaled nitric oxide were studied, while delivering these concentrations in random order for intervals of 20 to 30 mins. Each interval was preceded by an interval of 20 to 30 mins without nitric oxide. Patients were then randomized and treated for a prolonged period with approximately 10 or 40 ppm inhaled nitric oxide independent of their initial acute responses to 11 and 60 ppm. Nitric oxide was discontinued when ventilatory support was decreased to a PEEP of < or = 6 cm H2O and an FIO2 of < or = 0.5.

MEASUREMENTS AND MAIN RESULTS

Inhaled nitric oxide selectively decreased pulmonary vascular resistance and improved systemic oxygenation. Acute hemodynamic and blood gas effects of 11 and 60 ppm nitric oxide were similar. Systemic oxygenation improved to a greater extent in patients with radiographic evidence of residual aerated lung regions than in patients with diffuse bilateral lung disease. Maximum methemoglobin concentrations were greater in patients treated for a prolonged period with 40 ppm nitric oxide. The mortality and duration of therapy were similar for patients treated with 10 and 40 ppm inhaled nitric oxide.

CONCLUSIONS

Pulmonary vascular resistance and systemic oxygenation are acutely improved to a similar extent by 11 and 60 ppm inhaled nitric oxide, and concentrations in excess of 10 ppm are probably not needed for prolonged therapy of children with severe lung disease.

Delivery and monitoring of inhaled nitric oxide

Inhaled nitric oxide is rapidly gaining popularity as a selective pulmonary vasodilator in patients with acute lung injury and pulmonary hypertension. The development of nitric oxide as a drug has bypassed the usual regulatory and commercial processes, and as a result clinicians have devised a wide range of delivery and monitoring systems. This review describes these systems, and discusses their advantages, disadvantages and safety. The monitoring of nitric oxide metabolites is also discussed.

Nitric oxide: delivery, measurement, and clinical application

The biologic and therapeutic roles of NO are rapidly being elucidated. Before inhalational NO administration is commonplace, there is a clear need for consensus regarding safe and accurate delivery and measurement systems. The potential for NO usage appears large and potentially life-saving; yet multicenter trials need to carefully evaluate efficacy and safety.

Evaluation of a delivery system and monitors for ventilator administration of nitric oxide

The aim of this study was to compare nitric oxide (NO) and nitrogen dioxide (NO2) measurements obtained by chemiluminescence and electrochemical monitors using a delivery system for ventilator administration of NO. The formation of NO2 in this system and the efficacy of a soda-lime absorber to scavenge NO2 from inspiratory gas were also evaluated. Various concentrations of NO without and with soda lime were administered to a model lung via a Servo ventilator 900C with controlled ventilation by setting mass-flow regulators to maintain desired concentrations of NO in 80% O2. Close correlations were found between NO concentrations, as well as NO2 concentrations, measured using electrochemical monitors (TM100; 1002, PACII) and a chemiluminescence monitor (CLA-510SS). Soda-lime removed NO2 almost completely during administration of 0-25 p.p.m. NO, although a high concentration of NO2 appeared in the breathing circuit without soda lime. Four hundred grams of soda lime continued to absorb NO2 effectively during long-term administration of inhaled NO.These findings suggest that electrochemical monitoring is accurate and clinically useful for measurements of NO and NO2 concentrations, and that low doses of inhaled NO can be administered safely and reliably with the NO delivery system using a soda-lime absorber and mass-flow regulators.

Nitric oxide administration using constant-flow ventilation

Nitric oxide (NO) gas is known as both a vasodilator and a toxin. It can react with oxygen to form compounds more toxic than itself, such as nitrogen dioxide (NO2). The reactions are time dependent; thus, infusing NO into breathing circuits as close to ventilated subjects as possible may help minimize toxic byproduct exposure. Unfortunately, flow rates commonly used with mechanical ventilation favor laminar gas flow (streaming) within the breathing circuits. Streaming could delay mixing of NO with other inhaled gases. This mixing delay may interfere with accurate monitoring and/or delivery of NO. We tested the hypothesis that streaming of NO infused by constant flow into the inspiratory limb of a constant-flow mechanical ventilation system can lead to NO concentration delivery estimate errors. We then compared the NO2 concentrations at the ventilator Y-piece with three different NO mixing methods: blending the gases before they reach the breathing circuit inspiratory limb, infusing NO directly into the breathing circuit inspiratory limb far enough from the Y-piece to ensure thorough mixing, and infusing NO directly into the breathing circuit inspiratory limb immediately before the gases reach an in-line mixing device placed close to the Y-piece. Our results indicate that streaming can lead to NO concentration delivery estimate errors and that these errors can be characterized by measuring NO concentration variations across the inspiratory tubing's luminal diameter. NO2 concentration measured at the ventilator Y-piece were dependent on NO concentrations (p < 0.0001), NO delivery methods (p < 0.0001), and interactions between NO concentrations and NO delivery methods (p < 0.0001). We conclude that gas streaming and toxic byproduct exposure should be considered together when choosing an NO delivery method.

Inhaled nitric oxide in infants with developing or established chronic lung disease

The effect on gas exchange of increasing concentrations of nitric oxide (0-60 parts per million) added to the inspired gases of nine ventilator-dependent infants (median postnatal age = 4 weeks; range 2-16 weeks) with chronic lung disease and pathological oxygenation index values was studied by means of arterial or transcutaneous PO2/PCO2. A significant improvement of oxygenation, indicated by a reduction of oxygenation index, was found (p < 0.014). The optimal nitric oxide concentration and the individual response varied between patients. PO2 returned to baseline values after the discontinuation of nitric oxide in all patients except one. No effect on PCO2 could be identified. Methaemoglobin values only increased marginally during the nitrous oxide exposition (pre-nitric oxide: 0.56% +/- 0.27; post-nitric oxide: 0.78 +/- 0.08; p = ns). Systemic blood pressure and heart rate were unaffected in all patients. Before inhaled nitric oxide can be considered for prolonged use in this patient category further studies regarding long-term efficacy and safety are needed.

Comparison of two administration techniques of inhaled nitric oxide on nitrogen dioxide production

The purpose of this study was to verify whether, compared with the introduction of the NO-N2 mixture at the air inlet of the ventilator (classical method), a direct injection of NO-N2 into the inspiratory line of the ventilator circuit with a new injection device (new method), would reduce NO2 formation by reducing contact time between O2 and NO. The effect of two FIO2(0.21 and 0.90) and NO concentrations on NO2 production was determined. In the classical method, NO and O2 were mixed with an air/oxygen blender before the gas mixture entered the ventilator. In the new method, NO was injected directly into the respiratory line with the injection system. Nitric oxide and nitrogen dioxide gases were measured using a chemiluminescence analyzer. For a FI02 of 0.90 and 90 ppm of NO2, the amount of NO2 produced was decreased from 8.9 +/- 0.8 ppm (mean +/- SD) with the classical injection system to 4.4 +/- 0.2 ppm with the new injection system (P = 0.0039, Mann-Whitney test), and NO2 production was decreased from 4.5 +/-0.2 ppm to 2.1 +/- 0.4 ppm (P = 0.02) at 60 ppm of NO. However, at a FIO2, no difference was found in the amount of NO2 produced. We conclude that, compared with the classical method of NO administration, the new NO injection system reduces considerably the concentration of inhaled NO2 when a high FIO2 and a high concentration of NO are used.

Validation of a simple method assessing nitric oxide and nitrogen dioxide concentrations

Monitoring of nitric oxide (NO) and nitrogen dioxide (NO2) is a prerequisite for the clinical use of NO. Chemiluminescence, the reference method, cannot be used as a routine in clinical practice in view of its cost and other restraints. This study was performed to evaluate a device using an electrochemical method (Polytrons NO and NO2, Dräger). Forty-nine simultaneous measurements of NO and various oxides of nitrogen (NOx) concentrations by the two apparatus were performed. NO measurements by means of these two methods are very well correlated (r = 0.96; p < 10(-5)). The mean difference according to the method of Bland and Altman was 2.8 +/- 1.7 ppm, with the limits of agreement at -0.6 and +6.2 ppm (confidence interval of 95%). There was also a good correlation between measurements of NO2 obtained via Polytrons and NOx via chemiluminescence (r = 0.84; p < 10(-5)). However, NO2 measurements obtained via Polytrons may be insufficient to exclude potential toxicity of NO2 due to the inability to detect measurements in the ppb-range. This study demonstrates that devices designed for industrial purposes (Polytrons NO and NO2, Dräger) can be used for clinical purposes.

Conversion of inhaled nitric oxide to nitrate in man

1. Nitric oxide (NO) is potentially useful as a selective vasodilator drug in infants and adults with pulmonary hypertension. In vitro and in vivo observations demonstrate that NO may be converted to nitrate in the blood, to be further excreted into the urine. The aim of the present study was to assess quantitatively the importance of this pathway for inhaled NO in human subjects. 2. Healthy subjects inhaled 15NO (25 p.p.m.) for 1 h. The plasma and urine levels of 15NO3- were followed for 2 and 48 h, respectively. 3. The measured retention of 15NO in the lungs was 224 +/- 13 mumol, corresponding to 90 +/- 2% of the inhaled amount. Plasma 15NO3- increased during the inhalation of 15NO, to about 15 mumol l-1, and fell when inhalation of 15NO was terminated. 4. Urinary excretion of 15NO3- during the first 24 h after inhalation was 154 +/- 12 mumol. During the following 24 h another 8 +/- 2 mumol of 15NO3- appeared in the urine. 5. We conclude that conversion of inhaled NO to nitrate is a major metabolic pathway in man, covering more than 70% of its inactivation. The metabolic fate of the remaining NO inhaled requires further study.

Clinical applications of inhaled nitric oxide in children with pulmonary hypertension

We have presented our experience with the use of inhaled nitric oxide in children with congenital heart disease and pulmonary hypertension, which indicates that nitric oxide is a selective pulmonary vasodilator that may improve patient management, particularly after surgical procedures requiring cardiopulmonary bypass. Indeed, we have now seen several patients in whom all resuscitative maneuvers for the treatment of pulmonary hypertensive crises were unsuccessful until inhaled nitric oxide was added to the therapeutic regimen. In addition, our studies using inhaled nitric oxide as an investigational probe point toward endothelial injury as a contributor to post-cardiopulmonary bypass pulmonary vasoconstriction. Inhaled nitric oxide relieves pulmonary vasoconstriction associated both with left atrial or pulmonary venous hypertension and following the relief of mitral valve or pulmonary venous obstruction. Absence of a response on the usually reactive pulmonary vascular bed of the neonate should prompt a careful search for anatomic, and possibly surgically remediable, pulmonary vascular obstruction. In the short term nitric oxide is less effective in the older patient with obliterative pulmonary vascular disease. It is possible that recent experimental work with long-term nitric oxide inhalation might be applicable to this group of patients. Nitric oxide may have a unique role in the management of the patient after lung transplantation, as it both reduces right ventricular afterload and improves intrapulmonary shunting. Is nitric oxide the ideal agent for testing pulmonary vascular reactivity? Nitric oxide is simple to deliver by either mask or ventilator and, as a trial of vasoreactivity over 15 min, remains free of side effects that might be encountered during long-term administration, such as methemoglobinemia or nitrogen dioxide toxicity. Indeed, no patient developed significant methemoglobinemia after a trial of nitric oxide and neither was a level of nitrogen dioxide above 1 ppm registered during the administration. Thus, nitric oxide gas fulfills many of the ideal characteristics, as suggested by Rubin,92 required of a drug to test the acute responsiveness of the pulmonary circulation. It has better pulmonary dilating effects than systemic, a short half-life, and minimal adverse effects and it can be both easily and quickly administered. Whether it is able to reliably predict the effect of long-term administration of orally active agents awaits confirmation. Certainly, inhaled nitric oxide is rapidly becoming the standard agent to test pulmonary vascular reactivity during diagnostic cardiac catheterization at our institution.

Inhaled nitric oxide in neonates and children with pulmonary hypertension

Fourteen critically ill neonatal and paediatric intensive care patients with various primary diagnoses and signs of associated pulmonary hypertension received inhaled nitric oxide (NO), 20-80 ppm, after failure of conventional therapy to improve oxygenation. NO administration was found to be associated with a significant improvement in postductal arterial oxygen tension (pre-NO: 3.75 (SD 1.39) kPa; post-NO: 6.05 (SD 1.70) kPa; p = 0.004). In 10 patients, NO was found to increase arterial oxygen tension with more than 1 kPa. In 2 of these patients, ECMO treatment could be avoided due to the pronounced improvement in gas exchange seen after the initiation of NO administration. The remaining 4 patients failed to respond to NO administration. One patient developed methaemoglobinaemia (13.9%) which required treatment with methylthionine. Since we were unable to produce any beneficial effect of NO in the late phase of the pulmonary disease process, we believe that, in order to be successful, inhaled NO should be instituted when conventional treatment has failed and the administration of an iv vasodilator is usually considered.